Process for solvent extraction of aromatics from aromatic-paraffinic hydrocarbon mixture



May 2, 1967 H. P. HEBE RT 3,317,423

PROCESS FOR SOLVENT EXTRACTION OF AROMATICS FROM AROMATIC-PARAFFINICHYDROCARBON MIXTURE Filed Sept. 22, 1964 56 CONDENSER 53 4 PREHEATER IRAFHNATE STRIPPING 64 TOWER v REBOILER z; STEAM O f LEAN 58 RECYCLE ,I8RAFFINATPE' EXTRACTER FURFURAL OIL IO l2 ALKYL ATE FEED MA E UP 1 2| 721 RECYCLE CONDENSER I 42 ALKYLATE 4O I 1 I 3 \HJ '7' n PREHEATER EXTRACTSTRIPPING TOWER REBOILER STEAM 28h LEAN 'EXTRACT INVENTOR HUGH P- HEBERTmV ATTORNEY.

hydrocarbons, e.g., heavy United States Patent 3,317,423 PROCESS FORSOLVENT EXTRACTION OF ARO- MATICS FROM AROMATIC-PARAFFINIC HY- DROCARBONMIXTURE Hugh P. Hebert, Princeton, N.J., assignor to Cities Service OilCompany, a corporation of Delaware Filed Sept. 22, 1964, Ser. No.398,193

4 Claims. (Cl. 208327) "conducted at temperatures wherein both theraffinate and extract are in a fluid, easily handled liquid phase. The

aromatic hydrocarbons are dissolved by the solvent and separated fromthe mixture as the rich extract phase from which the aromatics arefurther separated by distillation and, in a commercial process, thesolvent is recirculated to the extractor. The parafiinic and naphthenichydrocarbons from the raffinate phase which also contain smallquantities of the solvent are also generally processed by distillationin a commercial process with the solvent being recirculated to theextractor.

In the extraction of aromatics from relatively heavy gas oil, decantoil, etc., by the above procedure the temperature is often above 140 F.since at lower temperatures the rafiinate is a viscous or semi-solidgelatinous material which is difiicult to handle. When furfural is usedas the solvent with the relatively heavy hydrocarbons at thetemperatures required to keep the raffinate in a fluid liquid phase, thearomatic extract has low BMCI values. Additionally, separation of therelatively expensive furfural in the extract and in the rafiinate bydistillation requires a substantial amount of steam.

It is an object of this invention to provide a process for preparing acarbon black feedstock having a high BMCI from relatively heavyhydrocarbons such as those boiling above 500 F.

It is another object of this invention to provide an economical processfor preparing a high quality carbon black feedstock from hydrocarbonsboiling above 500 F.

and economically separating the expensive solvent from the extract andraffinate phases by using furfural and a parafiinic hydrocarbon as dualsolvents at relatively low extraction temperatures and separating thefurfural together with the paraflinic solvent from the rafiinate andextract.

In accordance with a preferred embodiment of this invention, furfuraltogether with certain paratfinic hydrocarbon solvents are employed asdual solvents for the extraction of aromatics from relatively heavyhydrocarbons at extraction temperatures below 140 F. The paraffinichydrocarbon prevents gelling of the raffinate at these lowertemperatures and facilitates extraction at lower temperatures with aconsequent higher quality aromatic extract. Also the paraflinichydrocarbon acts as a chaser for the furfural in distillations of theraftinate and extract phases which facilitates recovery of the furfural.The paraflinic solvent and furfural are separated from each other afterthe distillation by settling and decantation of the condensate offurfural and parafiinic solvent from the distillation. It should benoted that extraction at the lower temperaturesv produce a higherquality aromatic concentrate irrespective of the parafiinic hydrocarbon.Thus, extraction at 80 F. with furfural and the paraffinic solvent givesa concentrate having a higher BMCI value than such an extraction at F.or 140 F.

Furfural is found to be more selective for the heavy aromatics at thelower temperatures. The paraffinic solvent also serves to stripparaflinic and naphthenic hydrocarbons from the rich extract phase andthus to further increase the quality of the aromatic extract.

The term BMCI as used herein is the abbreviation for the Bureau of MinesCorrelation Index which is used to designate the quality and suitabilityof aromatic concentrates for carbon black production.

The double solvent system of this invention can be used in any suitableextraction system. For instance, the invention may be used in a singlestage operation where the furfural, oil and paraflinic solventarethoroughly mixed together and then the resultant two phases allowed toseparate in a settling tank and withdrawn separately, or in a continuousextraction system using an extraction column or contactor forcounter-current extraction, or a centrifugal extraction unit.

The relatively heavy hydrocarbon feedstock employed in this invention isone boiling above 500 F., preferably above 600 F. and containssignificant quantities of aromatic hydrocarbons (usually at least about20 weight percent) and of paraffinic hydrocarbons (usually at leastabout 5 weight percent). Illustrative of such feedstocks there can bementioned: heavy cycle oils, decant oils, virgin and coker heavy gasoils, and deasphalted gas oils. The aniline'nurnber of the feed can befrom about 90 to about 180 and preferably from about to 170.

The preferred solvent for aromatics in the process of this invention isfurfural. However, other normally liquid organic compounds whichpreferentially dissolve aromatic hydrocarbons from hydrocarbon mixturescontaining the same in admixture with paraffinic or naphthenichydrocarbons can also be employed. Thus another suitable solvent for thearomatics which can be employed in this invention is phenol.

The preferred solvents for parafiins are paraflinic solvents but othersolvents which preferentially dissolve paraffin hydrocarbons from theabove feedstock and are immiscible with the selected solvent foraromatics may be used.

Furfural is preferably used in ratios of about 0.1 to 5.0 volumes pervolume of the relatively heavy hydrocarbon feedstock, preferably about0.5 to 2.0 volumes. However. volume ratios beyond these may also beused.

The paraflinic solvent can be any paratfinic hydrocarbon oil within theboiling range of about250 F. to about 400 F. and preferably having aboiling range of about 300 F. to about 375 F. A saturated hydrocarbonsuch as heavy alkylate obtained from isobutane and propylene or butyleneor amylene alkylation is particularly suitable as the parafiinicsolvent. The volume of the paraffinic solvent can vary beneath 0.05 and5.0 volumes per volume of feedstock (oil) and preferably between about0.1 and 2.0, however, volume ratios beyond these can be employed.

The temperature range in the extractor can be from about 50 F. to 140F., preferably from about 60 F. to about F. However, for optimum BMCIvalues it is preferred to use a temperature below 100 F. such as thatfrom about 70 F. to about 95 F. Temperature differentials in theextraction unit can be attained by varying the temperature of the feedstreams.

In a continuous extraction column the feed stock is preferably fed nearthe center, furfural near the rafiinate exit point and alkylate near theextract exit. The feed injection points can be varied to change thequality of the eflluent streams as desired. As mentioned hereinbefore,the extraction unit can also be a single stage mixer settler unit.Mixing in this latter case can be accomplished either with a mixingvalve, centrifugal pump or with an impeller.

The accompanying drawing shows a preferred embodiment of the process.The relatively heavy hydrocarbon feedstock, as described hereinbefore,is charged into extraction column 12 through line intermediate the topand bottom of the column and contacted therein under counter-currentflow conditions with furfural. The furfural is charged into the upperportion 14 of column 12 through line 18. Extraction column 12 has asuitable arrangement of conventional liquid-extraction equipment, notshown in the drawing, designed to obtain intimate contact between theliquid feedstock and liquid solvent.

A parafiinic solvent as described hereinbefore contacts the rich extractunder counter-current fiow conditions in the extractor 12 to displacehigher boiling feedstock paraffins from the rich extract stream prior toremoval of the rich extract from the extraction column and to lower theviscosity of the rafiin'ate phase. The paraflinc solvent is charged intothe process flow through line 20. Provisions are made in lines 18 and 20for the introduction of furfural and alkylate make up through lines 68and 21, respectively.

Due to the selective solubility of the aromatic component in thefurfural solvent relative to other hydrocarbons in the feed stock, thearomatics tend to transfer into a solvent phase leaving a solventimmiscible hydrocarbon rafiinate phase relatively lean in aromatics andcomprising other classes of hydrocarbons such as parafiins present inthe feedstock. The relatively dense extract phase gravitates downwardlyinto the lower portion of column 12 flowing counter-currently against astream of the paraffinic solvent tending to flow into the upper portionof column 12.

The rich extract phase which tends to flow downwardly through the columndue to its relatively greater density in comparison to the hydrocarbonfeedstock is withdrawn from the bottom of extraction column 12 throughline 16. It is then heated in preheater 22 and transferred through line24 into extract stripping tower 26. The extract stripping tower, as wellas the raifinate stripping tower which will be mentioned hereinafer, canbe any of several types of fractionation towers suited for stripping thelower boiling furfural (B.P. 329 F.) and paraflinic solvent (B.P. 250 F.to 400 F.) from the higher boiling hydrocarbon feed (boiling above 500F.). Extract stripping tower 26 is heated at a temperature suflicient todistill oif the furfural and paraffinic solvent from the aromatics. Thepreferred paraflinic solvent boils at about the same or slightly highertemperatures (300 F. to 375 F.) than the furfural and acts as astripping agent for furfural, thus reducing the need for steamstripping. The solvents pass out of stripping tower 26 through thecondenser 38 wherein they are cooled and condensed to the liquid phaseand subsequently drawn through line 40 into settling tank 42 where thesolvents separate into two distinct phases at temperatures of from about80 F. to about 120 F. The upper phase in separator 42 is the paraifinicsolvent and this is drawn off and conducted into .line 20 for recyclinginto extraction column 12. A portion of such solvent may be recycled tothe tower 26 through a line 72. Provision is made for adding paraffinicsolvent to line 20 for makeup. The lower phase in the separator 42 isfurfural which may be recycled to the extractor 12 via lines 65 and 18.Lean extract comprising the aromatic fraction from the rich solventphase is removed from stripping tower 26 through lines 28 and 34. Aportion of the lean extract is heated in a reboiler 32 and recirculatedinto the bottom of the extract stripping tower through a line 30 inorder to maintain distillation temperature.

The rafiinate from extractor 12 is heated in a preheater 48 andconducted to stripping tower 50 through a line 46. Lean rafiinate isconducted out of the bottom of this tower. A portion of the leanraflinate is heated in a reboiler 62 and recirculated into the lowerportion via a line 60 whereas the remainder is passed out of the processthrough a line 58. The paraifinic solvent and furfural are passed offoverhead in the vapor phase from the rafiinate stripping tower 50through a line 52, through a condenser 53 and into a settling tank 54where the two liquid solvents separate into a lower furfural phase andan upper paraffinic solvent phase. The parafiinic solvent is drawn oilthe top of the settling tank through a line 56 and is fed into recyclealkylate line 20 except for a portion returned to tower 50 through aline 71. The furfural from the bottom of tank 54 is passed through lines64 and 18 for recycling into the extractor.

The rich solvent phase conducted out of extractor 12 contains minorquantities of paraffinic solvent which is easily separated in theprocess. The rafiinate phase conducted out of extractor 12 can containminor quantities of furfural which is also easily separated in theprocess. The separation of the furfural and parafiinic solvent from boththe rich extract and the raffinate phase is performed by distillationwherein the paraffinic solvent aids in the stripping off of the moreexpensive furf-ural. The paraffinic solvent and furf-ural are theneasily separated from each other by settling. The rich extract phasewill often contain from about 5% to about 25% of parafiinic solvent byvolume but normally from about 8% to about 20% of paraffinic solvent byvolume. The rafiinate from the extractor can contain from about 0.5% toabout 10% of furfnral by volume and normally from about 1% to about 6%by volume of furfural.

Example I A selective solvent extraction system embodying the preferredarrangement of apparatus described in the accompanying diagrammaticdrawing is provided for the extraction of decant oil having a gravity of14.1" API, an initial boiling point of 605 F., and containing more than20 weight percent aromatics and more than 5 weight percent parafiins, bythe use of furfural and a paraffinic solvent having a boiling range offrom about 300 F. to about 375 F. This parafiinic solvent is a heavyalkylate fraction prepared from the alkylation of isobutane andpropylene.

Decant oil at a rate of 1,000 barrels per day (b.p.d.) is fed into themidsection of extractor 12 from line 10. Furfural at the rate of 500b.p.d. is fed into the upper portion of extractor 12 through line 18whereas alkylate at the rate of 460 b.p.d. is fed into the bottomportion of extractor 12. The extractor 12 is maintained at atmosphericpressure and a temperature of F: Raffinate comprising paraffinic andnaphthenic hydrocarbons together with a major portion of alkylate and aminor portion of furfural fed into the extractor is drawn oif the top ofthe extractor through line 46. The rafiinate in line 46 is conductedinto the raffinate stripping tower 50 after the temperature of therafiinate is raised to 440 F. by 'preheater 48. The upper portion of therafiinate stripping tower is maintained at a temperature of 275 F.whereas the bottom of this tower is maintained at a temperature of 450F. Lean rafiinate containing the nonaromatic hydrocarbons of the feedand substantially free of the solvents is withdrawn from rafiinatestripping tower through line 58 and out of the process at a rate of618.5 b.p.d. The lean raifinate has an API gravity of 29.5 Thetemperature in the lower portion of the raflinate stripping tower ismaintained by recirculating a part of the lean ratfinate through line 60and heater 62.

The raflinate stripping stripping tower is maintained at 3 (p.s.i.a.)pounds per square inch absolute. The alkylate together with smallquantities of furfural is distilled out of tower 50 through line 52, andthe vapors are cooled in condenser 53'prior to introduction intosettling tank or tower 54 which is maintained at F. The condenser 53isalso provided with means, not shown in the drawing, for drawing thevacuum maintained in tower 5 50. The alkylate is drawn off the top ofsettling tank 54 at a rate of 328 b.p.d. through line 56 which joins there cycle alkylate feed line 20 whereas furfural is drawn off the bottomof tank 54 at a rate of 30 b.p.d. and is passed into furfural recycleline 18.

Extract, comprising aromatics in the decant feed, a major portion of thefurfural and a minor portion of the alkylate fed into extractor 12 iswithdrawn from the bottom of the extractor through line 16. This richextract is conducted into extract stripping tower 26 after being heatedto 440 F. by preheater 22. Extract stripping tower 26 is maintained at apressure of 3 p.s.i.a., a temperature of 260 F. at its upper portion and450 F. at its lower portion. Lean extract of aromatic hydrocarbonssubstantially free of furfural and alkylate is conducted out of thebottom of tower 26 through line 28. A portion of the lean extract isrecirculated into tower 26 after passing through reboiler 32 whereas theremainder of the lean extract is passed out of the process through line34 at the rate of 381.5 b.p.d. This lean extract has a BMCI of 147 and aspecific gravity of 1.1356. Furfural and small quantities of alkylateare distilled off in tower 26 and are conducted through condenser 38 andfinally into settler 42 which is maintained at 110 F. The alkylate formsthe upper phase in the settling tank or tower 42 and is drawn off at therate of 132 b.p.d. by line 20. The furfural settles to the bottom oftank 42 and is drawn off at the rate of 470 b.p.d. through line 65 whichfeeds into furfural recycle conduit 18.

Example II The following Table I shows the effect of temperature and theuse of a parafiinic solvent on values of extracts in the processing ofthe decant oil described in Example I above. The process employed wasthat of the above Example I except for the variables shown in the table.

TABLE I.YIELD AND BMCI VALUES ON EXTRACTS WITH AND WITHOUT ALKYLATEADDITION [Decant oil] Temp, Furlural Alkylate BMCI of F. Oil Oil Extract1 350375 F. Alkylate.

2 301375 F. Alkylate.

400 F. and finally separating the aromatic components from the furfural.

2. A process for producing an aromatic concentrate from hydrocarbonfeedstock boiling above 500 F. and containing at least about 20 weightpercent aromatic hydrocarbons and at least about 5 weight percentparaffinic hydrocarbons which comprises: (a) counter-currentlycontacting said feedstock in an extraction zone maintained at atemperature throughout said zone of from about F. to about F. withfurfural to extract the aromatic components therefrom, thereby forming aparaffinic rafiinate containing minor quantities of furfural and anaromatic extract containing minor quantities of parafiins from thefeedstock; (b) counter-currently contacting said extract in said zonewith a substantially saturated parafiinic hydrocarbon solvent having aboiling range of from about 250 F. to about 400 F., thereby strippingadditional parafiinic feedstock therefrom and removing a major portionof said parafiinic solvent and thus stripped paraflinic feedstock inadmixture with the rafiinate from said zone; (c) removing the aromaticextract together with a major portion of the furfural and a minorportion of the parafiinic solvent from said zone; (d) distilling thewithdrawn rafiinate mixture to separate a mixture of parafiinic solventand furfural therefrom; (e) distilling the withdrawn extract to separate a mixture of furfural and paraffinic solvent therefrom; (f)settling thus separated mixtures of furfural and paraiiinic solvent toform separate phases of furfural and parafiinic solvent; and (g)separately recovering furfural and parafiinic solvent from step (f).

3. The process of claim 2 in which the mixtures formed in steps (d) and(e) are treated by condutcing the distilled parafiini-c solvent andfurfural separated from the raflinate phase to a settling zonemaintained at a temperature of from about 70 F. to about 95 F. tothereby form in said settling zone an upper parafiin solvent phase and alower furfural phase, conducting the distilled furfural and parafiinsolvent separated from the extract phase to a settling zone maintainedat a temperature of from about 70 F. to about 95 F. to thereby form insaid zone an upper paraffinic solvent phase and a lower furfural phase,separately drawing off the parafiinic solvent phase from furfural phasein each of said settling zones and returning both the paraflnic solventand the furfural therefrom to the extraction zone.

4. The process of claim 3 wherein from about 0.1 to 5 volumes offurfural and from about 0.05 to 5 volumes of the paraffinic solvent areemployed per volume of hydrocarbon feedstock.

References Cited by the Examiner FOREIGN PATENTS 2/ 1959 Great Britain.

DELBERT E. GANTZ, Primary Examiner. H. LEVINE, C. R. DAVIS, AssistantExaminers.

1. A PROCESS FOR PRODUCING AN AROMATIC CONCCENTRATE FROM HYDROCARBONFEEDSTOCK BOILING ABOVE 500*F. AND CONTAINING SUGNIFICANT QUANTITIES OFBOTH PARAFFINIC AND AROMATIC CONSTITUENTS WHICH COMPRISES CONTACTINGSAID FEEDSTOCK IN A COUNTERCURRENT EXTRACTION ZONE MAINTAINED AT ATEMPERATURE THROUGHOUT SAID ZONE OF FROM ABOUT 70*F. TO ABOUT 95*F. WITHFURFURAL, THEREBY FORMING A PARAFFINIC RAFFINATE AND AN AROMATIC EXTRACTCONTAINING A SMALL AMOUNT OF PARAFFINS, COUNTER-CURRENTLY CONTRACTINGSAID EXTRACT IN SAID ZONE WITH A PARAFFINIC HYDROCARBON HAVING A BOILINGPOINT OF FROM ABOUT 250*F. TO ABOUT 400*F. AND FINALLY SEPARATING THEAROMATIC COMPONENTS FROM THE FURFURAL.